A21 Dike Support

Diavik Diamond Mines Inc. (DDMI) has leveraged Nuna’s experience on heavy civil projects, capability to budget and schedule, and ability to supply qualified personnel to make the A21 project grow in scope from a simple manpower provider to a vital part of the DDMI construction team.

Project Scope

Supply of labour, large mine equipment operators, and equipment to support DDMI and Bauer construction of the A21 dike cut-off wall, including raising dike elevation, pipe benches, and roads

Support and liaise between DDMI and the contractors of various multilingual cultures on the project who are performing functions such as cut-off wall foundation, marine and barge, engineers of record, electrical, site services, scaffolding and carpentry, survey, dike thermosiphons, mobile plant maintenance, and janitorial and logistics

Provision of backfilling services during vibrodensification to produce dike columns (which involves a vibro tool vibrating into the ground and consolidating the existing material; once the tool has reached the desired elevation, the hole is backfilled with 2 feet of material and vibrated again so the end result is a complete hard column)

Operation of water buggies and grout plant for dike curtain grouting

Provision of labour, concrete mixer trucks, and excavators

Development of trenches and installation of concrete templates for pre-drill rigs (BG30 and BG40)

Provision of crane services and excavator support to clear the spoils generated from dike cutter soil mixing (CSM) wall construction

Work comprised the initial construction of 5.5 linear kilometres of containment and subsequent raising of the PKC dam (5-metre to 15-metre lifts), which entailed blasting and excavation of the key trench to bedrock and/or permafrost, leveling with till material, and placement of HDPE liner locked in with a till plug. Structure comprised rock fill, liner bedding, liner, and placement of rock fill for thermal protection.

A418 Dike Construction, Dewatering & Pre-stripping

Kimberlite pipe A418 required construction of a water retaining dike and cut-off wall. The A418 dike is 1.2 kilometres long, located in water up to 32 metres deep, and required approximately 1.1 million cubic metres of rockfill.

The A418 dike joins the existing A154 dike, and construction methods similar to those used in A154 dike were utilized: various sizes of rockfill, a central plastic concrete cut-off wall, jet and curtain grouting, and installation of instrumentation. A significant crushing facility prepared much of the rock before placement using rock from the A154 open pit. The rockfill portion of the A418 dike was completed in 2005, and the cut-off wall was completed in 2006.

North Inlet Dike

The North Inlet Dike was constructed prior to the A154 dike and provided a test platform to confirm the cut-off wall constructability criteria. This project consisted of backfilling the core with granular material, vibrodensification, and jet grouting columns.

A154 Dike Construction, Dewatering & Pre-stripping

Located 20 metres below water off an island in Lac de Gras, the A154 kimberlite pipe required construction of a 3.8-kilometre-long, up to 25-metre-high dike to enclose a 1.5-square-kilometre area. Lac de Gras Constructors was awarded the construction contract in 2000.

During the 2001 season, 5,000,000 cubic metres of rock was excavated, and 6,000,000 tonnes of crushed granular aggregate was produced and placed to complete the dike. Excavation along the central core of the dike allowed the installation of a bentonite cut-off wall of 51,000 square metres.

Project Scope

Installation of turbidity curtains

Foundation preparation (dredging)

Placement of filter material on lake bed floor

Placement of embankment (3 types of materials)

Vibrodensification of materials

Excavation through central core to facilitate cut-off wall

Trenching on land and in shallow waters for cut-off wall in some areas

Placement of abutment insulations, which included thermosiphons, drainage, and toe berms

Relief wells and installation of geotechnical instrumentation.

Jet grouting was required along the entire length of the dike between the cut-off/bedrock interface and curtain grouting below the cut-off in the bedrock.

Early Works

Nuna’s involvement began early with its support of the advanced exploration stage through construction and into several years of operation activities, including the following.

Preparation of the exploration site and placement of site facilities

Installation of a remote development site comprising camps, shops, fuel storage, and mining supplies sufficient for a 10-month underground bulk sample program, which included drilling/blasting and muck of a decline adit

Annual winter road access construction and maintenance

Reverse circulation drill support for an extensive annual drilling program, which included establishing drill pads on the Lac de Gras ice

Preparation and transportation of a 3,000-tonne bulk sample from the A154 site to the pilot plant in Yellowknife